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Statistics questions, answered
Plain-language answers to statistics questions people are asking. Have your own? Ask us.
Interrupted time series vs event study vs difference-in-differences
All three estimate the effect of an intervention, but each builds its counterfactual differently. Here is how to tell them apart.
Read the answer →Is a normality test worth running on your data?
Normality tests answer the wrong question: with lots of data they flag harmless quirks, with little data they miss real problems. Here is what to do.
Read the answer →What does kurtosis actually tell you about your data?
Kurtosis describes how heavy a distribution's tails are, not how peaked it is. Here is how to read it, in plain language.
Read the answer →Where does the 1/sqrt(n) margin of error come from?
The rule that a poll has a margin of error of about 1/sqrt(n) is a short derivation, not a guess. Here it is step by step.
Read the answer →Why does standard deviation square the differences?
Squaring deviations makes variances add up, ties into least squares and the normal distribution, and keeps the math clean.
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